Follow-up of the multinational phase 3 KATHERINE trial of trastuzumab emtansine versus trastuzumab for residual HER2-positive breast cancer

The multinational phase 3 KATHERINE trial randomized patients with HER2-positive breast cancer and residuale disease in breast or axilla after neoadjuvant therapy 1:1 to 14 cycles of trastuzumab emtansine (T-DM1) or trastuzumab. Results after a median follow-up of 8.4 years have now been published. T-DM1 sustained the previously reported improvement in invasive disease-free survival (IDFS) over trastuzumab (HR 0.54; 95% CI 0.44-0.66) with seven-years IDFS rates of 80.8% versus 67.1%. T-DM1 alos led to a significantly lower risk of death than trastuzumab (HR 0.66; 95% CI 0.51-0.87) with seven-year overall survival rates of 89.1% versus 84.4%. Adverse events of grade 3 or higher were noted in 26% of patients in the T-DM1 group and 15.7% of patients in the trastuzumab group. The authors conclude that, as compared with trastuzumab, T-DM1 improved overall survival with sustained improvement in IDFS among patients with HER2-positive early breast cancer with residual invasive disease after neoadjuvant therapy.